The present inaction relates to a method for manufacturing semiconductor devices whilst measuring the thickness and thickness distribution of transparent film and controlling the film thickness, for example, a method for measuring uppermost film thickness of a wafer in a surface levelling process stage after film deposition, the levelling process stage in the manufacture of a semiconductor device being controlled by measuring the film thickness. Examples of such transparent films include, in addition to the foregoing, resist films and insulating films, and the like, in manufacturing stages of thin film devices, such as DVD, TFT and LSI reticles, and the like.
For example, semiconductor devices are manufactured by forming devices and wiring patterns onto a silicon wafer, by means of film deposition, exposure and etching processes. In recent years, in order to achieve higher precision and higher density in such devices, there have been moves towards greater fineness and increased layering. This has resulted in an increase in the number of indentations in the wafer surface. Such indentations in the wafer impede the light exposure process, which is essential in forming wiring, and the like, and therefore levelling of the wafer surface is carried out. A CMP (Chemical Mechanical Polishing) technique, wherein the surface of the wafer is levelled by polishing based on chemical and physical actions, is used for this levelling process. CMP is a commonly known technique in the related technological field.
The principal problem involved with CMP processing is that of controlling film thickness. In particular, it is necessary to reduce variation in the high-precision evenness and film thickness of the wafers by incorporating an in-situ measuring system into the CMP system in order to measure the film thickness during the CMP process, and halting the process when the wafer has been processed to a prescribed film thickness. Consequently, a variety of methods have been proposed as in-situ measurement techniques.
Japanese Patent Laid-open No. (Hei)6-252113 and Japanese Patent Laid-open No. (Hei)9-7985 disclose in-situ measuring systems capable of measuring the film thickness over the actual device pattern (at the fine circuit pattern constituting the actual product). In Japanese Patent Laid-open No. (Hei)6-252113, in measuring the film thickness over the actual device pattern, the spectrum of the interference pattern produced by the film from white light is analyzed with respect to frequency, and the absolute value of the thin film is calculated by observing the relationship between the frequency component relating to the spectral waveform and the film thickness. On the other hand, in Japanese Patent Laid-open No. (Hei)10-83977, the change with respect to processing time of the intensity of the interference pattern produced by the transparent film from a laser (single-wavelength source) is detected and the film thickness is calculated from the frequency component relating to that waveform.
Moreover, Japanese Patent Laid-open No. (Hei)10-294297 and Japanese Patent Laid-open No. 2000-77371 disclose techniques for performing in-situ measurement by specifying measurement positions. In Japanese Patent Laid-open No. (Hei)10-294297, the measurement positions are specified by extracting the characteristics of the image of the circuit pattern, or by forming a diffraction pattern in the scribe area of the pattern. In Japanese Patent Laid-open No. 2000-77371, the maxima and minima of the spectral waveform are observed, and measurement points for measuring the film thickness during processing are specified by comparison of these with previously measured maxima and minima of spectral waveforms.
Generally, there have been problems in managing film thickness to a high degree of accuracy by means of the CMP processing time, since the polishing amount (polishing rate) per unit time varies, and the polishing rate also differs according to the ratio of the wafer plane occupied by the pattern formed thereon (hereinafter, called “pattern area ratio”). FIG. 17 shows the film thickness distribution measurement results for a semiconductor device measured using the technique disclosed in Japanese Patent Laid No. 2000-310512. FIG. 17 illustrates film thickness distribution measurement results 160 for a transparent film (insulating film between layers) having an area of approximately 20 mm on a wafer that has been CMP processed. FIG. 17 shows the film thickness distribution in the wiring pattern sections 161, 162, peripheral circuit section 163, and the border section 164, 165 between the peripheral circuit section and the wiring pattern sections. As these film thickness distribution measurement results 160 show, a film thickness change of several 100 nm occurs in a region of approximately 2 mm at the border sections 164, 165 between the peripheral circuit sections and the wiring pattern sections. On the other hand, the wiring patterns sections 161, 162 and the peripheral circuit section 163 themselves has a comparatively even film thickness over regions of several mm.
This film thickness distribution is produced by the pattern area ratio, and processing conditions such as the type of polishing pad in the processing device, the type of polishing fluid (slurry), and the like, and it may vary between products or between each wafer, due to variations in the type of semiconductor or circuit pattern, and in the processing conditions (state of wear of the polishing pad, density of slurry, and the like). As described above, in in-situ measurement during the CMP process, a problem arises in that, depending of the observed field being measured, the measurement accuracy declines as regions having great variation in film thickness are measured. Furthermore, although Japanese Patent Laid-open No. (Hei)10-294297 and Japanese Patent Laid-open No. 2000-77371 disclose methods for specifying measurement points, even in these disclosures, no particular attention is given to the measurement fields, which are specified over a relatively large region (diameter of approximately 2 mm), and hence there is a risk that measurement accuracy will decline when the film thickness is measured in a state such as that illustrated in FIG. 17.
In other words, the spectral waveform provides waveform data including information from a broad area of varying film thickness and underside wiring state, and hence it is difficult to specify the desired measurement points. Therefore, it is not possible to reduce fluctuation in high-precision evenness and film thickness characteristics by terminating the CMP processing at the moment that the wafer has been processed to a prescribed film thickness, thereby making it difficult to control film thickness to a high degree of accuracy and hence leading to a decline in semiconductor device yield. Moreover, conventionally, slurry has been used as a polishing fluid in CMP processing.
As also disclosed in Japanese Patent Laid-open No. (Hei)10-83977, in-situ measurement is conducted by forming a transparent window in the polishing band and extracting the spectral waveform from the wafer surface in the slurry. Since the slurry is a polishing fluid containing particles of silica, potassium hydroxide, and the like, it is optically semi-transparent, and has poor light transmission characteristics. Furthermore, the spectral reflectivity of the wafer surface is also reduced markedly by the occurrence of glass-type indentations in the transparent window due to the action of the particles contained in the polishing fluid, and hence the spectrum cannot be measured in a stable fashion, thereby making it difficult to achieve high-precision control of the film thickness by terminating CMP processing at the moment that the wafer has been processing to a prescribed film thickness.